Greenhouse gas emissions from four bioenergy crops in England and Wales: Integrating spatial estimates of yield and soil carbon balance in life cycle analyses

Accurate estimation of the greenhouse gas (GHG) mitigation potential of bioenergy crops requires the integration of a significant component of spatially varying information. In particular, crop yield and soil carbon (C) stocks are variables which are generally soil type and climate dependent. Since gaseous emissions from soil C depend on current C stocks, which in turn are related to previous land management it is important to consider both previous and proposed future land use in any C accounting assessment. We have conducted a spatially explicit study for England and Wales, coupling empirical yield maps with the RothC soil C turnover model to simulate soil C dynamics. We estimate soil C changes under proposed planting of four bioenergy crops, Miscanthus ( Miscanthus × giganteus ), short rotation coppice (SRC) poplar ( Populus trichocarpa Torr. & Gray × P. trichocarpa , var. Trichobel), winter wheat, and oilseed rape. This is then related to the former land use – arable, pasture, or forest/seminatural, and the outputs are then assessed in the context of a life cycle analysis (LCA) for each crop. By offsetting emissions from management under the previous land use, and considering fossil fuel C displaced, the GHG balance is estimated for each of the 12 land use change transitions associated with replacing arable, grassland, or forest/seminatural land, with each of the four bioenergy crops. Miscanthus and SRC are likely to have a mostly beneficial impact in reducing GHG emissions, while oilseed rape and winter wheat have either a net GHG cost, or only a marginal benefit. Previous land use is important and can make the difference between the bioenergy crop being beneficial or worse than the existing land use in terms of GHG balance.     

Bioethanol production from sugarcane and emissions of greenhouse gases – known and unknowns

Bioethanol production from sugarcane is discussed as an alternative energy source to reduce dependencies of regional economies on fossil fuels. Even though bioethanol production from sugarcane is considered to be a beneficial and cost‐effective greenhouse gas (GHG) mitigation strategy, it is still a matter of controversy due to insufficient information on the total GHG balance of this system. Aside from the necessity to account for the impact of land use change (LUC), soil N₂O emissions during sugarcane production and emissions of GHG due to preharvest burning may significantly impact the GHG balance. Based on a thorough literature review, we show that direct N₂O emissions from sugarcane fields due to nitrogen (N) fertilization result in an emission factor of 3.87±1.16% which is much higher than suggested by IPCC (1%). N₂O emissions from N fertilization accounted for 40% of the total GHG emissions from ethanol–sugarcane production, with an additional 17% from trash burning. If LUC‐related GHG emissions are considered, the total GHG balance turns negative mainly due to vegetation carbon losses. Our study also shows that major gaps in knowledge still exist about GHG sources related to agricultural management during sugarcane production, e.g. effects of irrigation, vinasse and filter cake application. Therefore, more studies are needed to assess if bioethanol from sugarcane is a viable option to reduce energy‐related GHG emissions.     

Comparing annual and perennial crops for bioenergy production – influence on nitrate leaching and energy balance

Production of energy crops is promoted as a means to mitigate global warming by decreasing dependency on fossil energy. However, agricultural production of bioenergy can have various environmental effects depending on the crop and production system. In a field trial initiated in 2008, nitrate concentration in soil water was measured below winter wheat, grass‐clover and willow during three growing seasons. Crop water balances were modelled to estimate the amount of nitrate leached per hectare. In addition, dry matter yields and nitrogen (N) yields were measured, and N balances and energy balances were calculated. In willow, nitrate concentrations were up to approximately 20 mg l^?1 nitrate‐N during the establishment year, but declined subsequently to <5 mg l^?1 nitrate‐N, resulting in an annual N leaching loss of 18, 3 and 0.3 kg ha^?1 yr^?1 N in the first 3 years after planting. A similar trend was observed in grass‐clover where concentrations stabilized at 2–4 mg l^?1 nitrate‐N from the beginning of the second growing season, corresponding to leaching of approximately 5 kg ha^?1 yr^?1 N. In winter wheat, an annual N leaching loss of 36–68 kg ha^?1 yr^?1 was observed. For comparison, nitrate leaching was also measured in an old willow crop established in 1996 from which N leaching ranged from 6 to 27 kg ha^?1 yr^?1. Dry matter yields ranged between 5.9 and 14.8 Mg yr^?1 with lowest yield in the newly established willow and the highest yield harvested in grass‐clover. Grass‐clover gave the highest net energy yield of 244 GJ ha^?1 yr^?1, whereas old willow, winter wheat and first rotation willow gave net energy yields of 235, 180 and 105 GJ ha^?1 yr^?1. The study showed that perennial crops can provide high energy yields and significantly reduce N losses compared to annual crops.     

The European carbon balance. Part 4: integration of carbon and other trace‐gas fluxes

Overviewing the European carbon (C), greenhouse gas (GHG), and non‐GHG fluxes, gross primary productivity (GPP) is about 9.3 Pg yr^?1, and fossil fuel imports are 1.6 Pg yr^?1. GPP is about 1.25% of solar radiation, containing about 360 × 10¹⁸ J energy – five times the energy content of annual fossil fuel use. Net primary production (NPP) is 50%, terrestrial net biome productivity, NBP, 3%, and the net GHG balance, NGB, 0.3% of GPP. Human harvest uses 20% of NPP or 10% of GPP, or alternatively 1‰ of solar radiation after accounting for the inherent cost of agriculture and forestry, for production of pesticides and fertilizer, the return of organic fertilizer, and for the C equivalent cost of GHG emissions. C equivalents are defined on a global warming potential with a 100‐year time horizon. The equivalent of about 2.4% of the mineral fertilizer input is emitted as N₂O. Agricultural emissions to the atmosphere are about 40% of total methane, 60% of total NO‐N, 70% of total N₂O‐N, and 95% of total NH₃‐N emissions of Europe. European soils are a net C sink (114 Tg yr^?1), but considering the emissions of GHGs, soils are a source of about 26 Tg CO₂ C‐equivalent yr^?1. Forest, grassland and sediment C sinks are offset by GHG emissions from croplands, peatlands and inland waters. Non‐GHGs (NH₃, NOx) interact significantly with the GHG and the C cycle through ammonium nitrate aerosols and dry deposition. Wet deposition of nitrogen (N) supports about 50% of forest timber growth. Land use change is regionally important. The absolute flux values total about 50 Tg C yr^?1. Nevertheless, for the European trace‐gas balance, land‐use intensity is more important than land‐use change. This study shows that emissions of GHGs and non‐GHGs significantly distort the C cycle and eliminate apparent C sinks.     

模拟氮沉降对华西雨屏区苦竹林凋落物养分输入量的早期影响

2007年11月至2010年12月对华西雨屏区苦竹人工林进行了模拟氮(N)沉降试验,氮沉降水平分别为：对照(0 g N.m_–2.a_–1),低氮(5 g N.m_–2.a_–1),中氮(15 g N.m_–2.a_–1),高氮(30 g N.m_–2.a_–1)。在氮沉降2 a后,于2010年1月开始收集各样方的凋落物样品,连续收集12个月,测定凋落物量和养分输入量。结果表明：氮沉降显著增加了凋落物量;同时显著增加了凋落叶中的N、P、K、Ca、Mg元素含量和这几种养分元素的年输入量。本研究表明模拟氮沉降处理增加了凋落物对土壤养分的输入量,这对于维持苦竹林地肥力与保持苦竹林分的长期生长力具有重要的作用。     

Closing the yield gap could reduce projected greenhouse gas emissions: a case study of maize production in China

Although the goal of doubling food demand while simultaneously reducing agricultural environmental damage has become widely accepted, the dominant agricultural paradigm still considers high yields and reduced greenhouse gas (GHG) intensity to be in conflict with one another. Here, we achieved an increase in maize yield of 70% in on‐farm experiments by closing the yield gap and evaluated the trade‐off between grain yield, nitrogen (N) fertilizer use, and GHG emissions. Based on two groups of N application experiments in six locations for 16 on‐farm site‐years, an integrated soil‐crop system (HY) approach achieved 93% of the yield potential and averaged 14.8 Mg ha^?1 maize grain yield at 15.5% moisture. This is 70% higher than current crop (CC) management. More importantly, the optimal N rate for the HY system was 250 kg N ha^?1, which is only 38% more N fertilizer input than that applied in the CC system. Both the N₂O emission intensity and GHG intensity increased exponentially as the N application rate increased, and the response curve for the CC system was always higher than that for the HY system. Although the N application rate increased by 38%, N₂O emission intensity and the GHG intensity of the HY system were reduced by 12% and 19%, respectively. These on‐farm observations indicate that closing the yield gap alongside efficient N management should therefore be prominent among a portfolio of strategies to meet food demand while reducing GHG intensity at the same time.     

Trade‐offs across productivity,GHG intensity,and pollutant loads from second‐generation sorghum bioenergy

Greenhouse gas (GHG) intensity is frequently used to assess the mitigation potential of biofuels; however, failure to quantify other environmental impacts may result in unintended consequences, effectively shifting the environmental burden of fuel production rather than reducing it. We modeled production of E₈₅, a gasoline/ethanol blend, from forage sorghum (Sorghum bicolor cv. photoperiod LS) grown, processed, and consumed in California's Imperial Valley in order to evaluate the influence of nitrogen (N) management on well‐to‐wheel (WTW) environmental impacts from cellulosic ethanol. We simulated 25 N management scenarios varying application rate, application method, and N source. Life cycle environmental impacts were characterized using the EPA's criteria for emissions affecting the environment and human health. Our results suggest efficient use of N is an important pathway for minimizing WTW emissions on an energy yield basis. Simulations in which N was injected had the highest nitrogen use efficiency. Even at rates as high as 450 kg N ha^?1, injected N simulations generated a yield response sufficient to outweigh accompanying increases in most N‐induced emissions on an energy yield basis. Thus, within the biofuel life cycle, trade‐offs across productivity, GHG intensity, and pollutant loads may be possible to avoid at regional to global scales. However, trade‐offs were seemingly unavoidable when impacts from E₈₅ were compared to those of conventional gasoline. The GHG intensity of sorghum‐derived E₈₅ ranged from 29 to 44 g CO₂ eq MJ^?1, roughly 1/3 to 1/2 that of gasoline. Conversely, emissions contributing to local air and water pollution tended to be substantially higher in the E₈₅ life cycle. These adverse impacts were strongly influenced by N management and could be partially mitigated by efficient application of N fertilizers. Together, our results emphasize the importance of minimizing on‐farm emissions in maximizing both the environmental benefits and profitability of biofuels.     

Large‐scale bioenergy from additional harvest of forest biomass is neither sustainable nor greenhouse gas neutral

Owing to the peculiarities of forest net primary production humans would appropriate ca. 60% of the global increment of woody biomass if forest biomass were to produce 20% of current global primary energy supply. We argue that such an increase in biomass harvest would result in younger forests, lower biomass pools, depleted soil nutrient stocks and a loss of other ecosystem functions. The proposed strategy is likely to miss its main objective, i.e. to reduce greenhouse gas (GHG) emissions, because it would result in a reduction of biomass pools that may take decades to centuries to be paid back by fossil fuel substitution, if paid back at all. Eventually, depleted soil fertility will make the production unsustainable and require fertilization, which in turn increases GHG emissions due to N₂O emissions. Hence, large‐scale production of bioenergy from forest biomass is neither sustainable nor GHG neutral.     

Range and uncertainties in estimating delays in greenhouse gas mitigation potential of forest bioenergy sourced from Canadian forests

Accurately assessing the delay before the substitution of fossil fuel by forest bioenergy starts having a net beneficial impact on atmospheric CO₂ is becoming important as the cost of delaying GHG emission reductions is increasingly being recognized. We documented the time to carbon (C) parity of forest bioenergy sourced from different feedstocks (harvest residues, salvaged trees, and green trees), typical of forest biomass production in Canada, used to replace three fossil fuel types (coal, oil, and natural gas) in heating or power generation. The time to C parity is defined as the time needed for the newly established bioenergy system to reach the cumulative C emissions of a fossil fuel, counterfactual system. Furthermore, we estimated an uncertainty period derived from the difference in C parity time between predefined best‐ and worst‐case scenarios, in which parameter values related to the supply chain and forest dynamics varied. The results indicate short‐to‐long ranking of C parity times for residues < salvaged trees < green trees and for substituting the less energy‐dense fossil fuels (coal < oil < natural gas). A sensitivity analysis indicated that silviculture and enhanced conversion efficiency, when occurring only in the bioenergy system, help reduce time to C parity. The uncertainty around the estimate of C parity time is generally small and inconsequential in the case of harvest residues but is generally large for the other feedstocks, indicating that meeting specific C parity time using feedstock other than residues is possible, but would require very specific conditions. Overall, the use of single parity time values to evaluate the performance of a particular feedstock in mitigating GHG emissions should be questioned given the importance of uncertainty as an inherent component of any bioenergy project.     

Contribution of N2O to the greenhouse gas balance of first-generation biofuels

In this study, we analyze the impact of fertilizer‐ and manure‐induced N₂O emissions due to energy crop production on the reduction of greenhouse gas (GHG) emissions when conventional transportation fuels are replaced by first‐generation biofuels (also taking account of other GHG emissions during the entire life cycle). We calculate the nitrous oxide (N₂O) emissions by applying a statistical model that uses spatial data on climate and soil. For the land use that is assumed to be replaced by energy crop production (the ‘reference land‐use system’), we explore a variety of options, the most important of which are cropland for food production, grassland, and natural vegetation. Calculations are also done in the case that emissions due to energy crop production are fully additional and thus no reference is considered. The results are combined with data on other emissions due to biofuels production that are derived from existing studies, resulting in total GHG emission reduction potentials for major biofuels compared with conventional fuels. The results show that N₂O emissions can have an important impact on the overall GHG balance of biofuels, though there are large uncertainties. The most important ones are those in the statistical model and the GHG emissions not related to land use. Ethanol produced from sugar cane and sugar beet are relatively robust GHG savers: these biofuels change the GHG emissions by −103% to −60% (sugar cane) and −58% to −17% (sugar beet), compared with conventional transportation fuels and depending on the reference land‐use system that is considered. The use of diesel from palm fruit also results in a relatively constant and substantial change of the GHG emissions by −75% to −39%. For corn and wheat ethanol, the figures are −38% to 11% and −107% to 53%, respectively. Rapeseed diesel changes the GHG emissions by −81% to 72% and soybean diesel by −111% to 44%. Optimized crop management, which involves the use of state‐of‐the‐art agricultural technologies combined with an optimized fertilization regime and the use of nitrification inhibitors, can reduce N₂O emissions substantially and change the GHG emissions by up to −135 percent points (pp) compared with conventional management. However, the uncertainties in the statistical N₂O emission model and in the data on non‐land‐use GHG emissions due to biofuels production are large; they can change the GHG emission reduction by between −152 and 87 pp.     

Implications of productivity and nutrient requirements on greenhouse gas balance of annual and perennial bioenergy crops

Biomass from dedicated crops is expected to contribute significantly to the replacement of fossil resources. However, sustainable bioenergy cropping systems must provide high biomass production and low environmental impacts. This study aimed at quantifying biomass production, nutrient removal, expected ethanol production, and greenhouse gas (GHG) balance of six bioenergy crops: Miscanthus × giganteus, switchgrass, fescue, alfalfa, triticale, and fiber sorghum. Biomass production and N, P, K balances (input‐output) were measured during 4 years in a long‐term experiment, which included two nitrogen fertilization treatments. These results were used to calculate a posteriori ‘optimized’ fertilization practices, which would ensure a sustainable production with a nil balance of nutrients. A modified version of the cost/benefit approach proposed by Crutzen et al. (2008), comparing the GHG emissions resulting from N‐P‐K fertilization of bioenergy crops and the GHG emissions saved by replacing fossil fuel, was applied to these ‘optimized’ situations. Biomass production varied among crops between 10.0 (fescue) and 26.9 t DM ha^?1 yr^?1 (miscanthus harvested early) and the expected ethanol production between 1.3 (alfalfa) and 6.1 t ha^?1 yr^?1 (miscanthus harvested early). The cost/benefit ratio ranged from 0.10 (miscanthus harvested late) to 0.71 (fescue); it was closely correlated with the N/C ratio of the harvested biomass, except for alfalfa. The amount of saved CO₂ emissions varied from 1.0 (fescue) to 8.6 t CO₂eq ha^?1 yr^?1 (miscanthus harvested early or late). Due to its high biomass production, miscanthus was able to combine a high production of ethanol and a large saving of CO₂ emissions. Miscanthus and switchgrass harvested late gave the best compromise between low N‐P‐K requirements, high GHG saving per unit of biomass, and high productivity per hectare.     

Abatement cost of wood‐based energy products at the production level on afforested and reforested lands

We combined economic and life‐cycle analyses in an integrated framework to ascertain greenhouse gas (GHG) intensities, production costs, and abatement costs of GHG emissions for ethanol and electricity derived from three woody feedstocks (logging residues only, pulpwood only, and pulpwood and logging residues combined) across two forest management choices (intensive and nonintensive) and 31 harvest ages (year 10–year 40 in steps of 1 year) on reforested and afforested lands at the production level for slash pine (Pinus elliottii) in the Southern United States. We assumed that wood chips and wood pellets will be used to produce ethanol and generate electricity, respectively. Production costs and GHG intensities of ethanol and electricity were lowest for logging residues at the optimal rotation age for both forest management choices. Opportunity cost related with the change in rotation age was a significant determinant of the variability in the overall production cost. GHG intensity of feedstocks obtained from afforested land was lower than reforested land. Relative savings in GHG emissions were higher for ethanol than electricity. Abatement cost of GHG emissions for ethanol was lower than electricity, especially when feedstocks were obtained from a plantation whose rotation age was close to the optimal rotation age. A carbon tax of at least $25 and $38 Mg^?1 CO₂e will be needed to promote production of ethanol from wood chips and electricity from wood pellets in the US, respectively.     

High‐resolution spatial modelling of greenhouse gas emissions from land‐use change to energy crops in the United Kingdom

We implemented a spatial application of a previously evaluated model of soil GHG emissions, ECOSSE, in the United Kingdom to examine the impacts to 2050 of land‐use transitions from existing land use, rotational cropland, permanent grassland or woodland, to six bioenergy crops; three ‘first‐generation’ energy crops: oilseed rape, wheat and sugar beet, and three ‘second‐generation’ energy crops: Miscanthus, short rotation coppice willow (SRC) and short rotation forestry poplar (SRF). Conversion of rotational crops to Miscanthus, SRC and SRF and conversion of permanent grass to SRF show beneficial changes in soil GHG balance over a significant area. Conversion of permanent grass to Miscanthus, permanent grass to SRF and forest to SRF shows detrimental changes in soil GHG balance over a significant area. Conversion of permanent grass to wheat, oilseed rape, sugar beet and SRC and all conversions from forest show large detrimental changes in soil GHG balance over most of the United Kingdom, largely due to moving from uncultivated soil to regular cultivation. Differences in net GHG emissions between climate scenarios to 2050 were not significant. Overall, SRF offers the greatest beneficial impact on soil GHG balance. These results provide one criterion for selection of bioenergy crops and do not consider GHG emission increases/decreases resulting from displaced food production, bio‐physical factors (e.g. the energy density of the crop) and socio‐economic factors (e.g. expenditure on harvesting equipment). Given that the soil GHG balance is dominated by change in soil organic carbon (SOC) with the difference among Miscanthus, SRC and SRF largely determined by yield, a target for management of perennial energy crops is to achieve the best possible yield using the most appropriate energy crop and cultivar for the local situation.     

A multi‐criteria based review of models that predict environmental impacts of land use‐change for perennial energy crops on water,carbon and nitrogen cycling

Reduction in energy sector greenhouse gas GHG emissions is a key aim of European Commission plans to expand cultivation of bioenergy crops. Since agriculture makes up 10–12% of anthropogenic GHG emissions, impacts of land‐use change must be considered, which requires detailed understanding of specific changes to agroecosystems. The greenhouse gas (GHG) balance of perennials may differ significantly from the previous ecosystem. Net change in GHG emissions with land‐use change for bioenergy may exceed avoided fossil fuel emissions, meaning that actual GHG mitigation benefits are variable. Carbon (C) and nitrogen (N) cycling are complex interlinked systems, and a change in land management may affect both differently at different sites, depending on other variables. Change in evapotranspiration with land‐use change may also have significant environmental or water resource impacts at some locations. This article derives a multi‐criteria based decision analysis approach to objectively identify the most appropriate assessment method of the environmental impacts of land‐use change for perennial energy crops. Based on a literature review and conceptual model in support of this approach, the potential impacts of land‐use change for perennial energy crops on GHG emissions and evapotranspiration were identified, as well as likely controlling variables. These findings were used to structure the decision problem and to outline model requirements. A process‐based model representing the complete agroecosystem was identified as the best predictive tool, where adequate data are available. Nineteen models were assessed according to suitability criteria, to identify current model capability, based on the conceptual model, and explicit representation of processes at appropriate resolution. FASSET, ECOSSE, ANIMO, DNDC, DayCent, Expert‐N, Ecosys, WNMM and CERES‐NOE were identified as appropriate models, with factors such as crop, location and data availability dictating the final decision for a given project. A database to inform such decisions is included.     

Forest bioenergy climate impact can be improved by allocating forest residue removal

Bioenergy from forest residues can be used to avoid fossil carbon emissions, but removing biomass from forests reduces carbon stock sizes and carbon input to litter and soil. The magnitude and longevity of these carbon stock changes determine how effective measures to utilize bioenergy from forest residues are to reduce greenhouse gas (GHG) emissions from the energy sector and to mitigate climate change. In this study, we estimate the variability of GHG emissions and consequent climate impacts resulting from producing bioenergy from stumps, branches and residual biomass of forest thinning operations in Finland, and the contribution of the variability in key factors, i.e. forest residue diameter, tree species, geographical location of the forest biomass removal site and harvesting method, to the emissions and their climate impact. The GHG emissions and the consequent climate impacts estimated as changes in radiative forcing were comparable to fossil fuels when bioenergy production from forest residues was initiated. The emissions and climate impacts decreased over time because forest residues were predicted to decompose releasing CO₂ even if left in the forest. Both were mainly affected by forest residue diameter and climatic conditions of the forest residue collection site. Tree species and the harvest method of thinning wood (whole tree or stem‐only) had a smaller effect on the magnitude of emissions. The largest reduction in the energy production climate impacts after 20 years, up to 62%, was achieved when coal was replaced by the branches collected from Southern Finland, whereas the smallest reduction 7% was gained by using stumps from Northern Finland instead of natural gas. After 100 years the corresponding values were 77% and 21%. The choice of forest residue biomass collected affects significantly the emissions and climate impacts of forest bioenergy.     

Plant roots and GHG mitigation in native perennial bioenergy cropping systems

Native perennial bioenergy crops can mitigate greenhouse gases (GHG) by displacing fossil fuels with renewable energy and sequestering atmospheric carbon (C) in soil and roots. The relative contribution of root C to net GHG mitigation potential has not been compared in perennial bioenergy crops ranging in species diversity and N fertility. We measured root biomass, C, nitrogen (N), and soil organic carbon (SOC) in the upper 90 cm of soil for five native perennial bioenergy crops managed with and without N fertilizer. Bioenergy crops ranged in species composition and were annually harvested for 6 (one location) and 7 years (three locations) following the seeding year. Total root biomass was 84% greater in switchgrass (Panicum virgatum L.) and a four‐species grass polyculture compared to high‐diversity polycultures; the difference was driven by more biomass at shallow soil depth (0–30 cm). Total root C (0–90 cm) ranged from 3.7 Mg C ha^?1 for a 12‐species mixture to 7.6 Mg C ha^?1 for switchgrass. On average, standing root C accounted for 41% of net GHG mitigation potential. After accounting for farm and ethanol production emissions, net GHG mitigation potential from fossil fuel offsets and root C was greatest for switchgrass (?8.4 Mg CO2e ha^?1 yr^?1) and lowest for high‐diversity mixtures (?4.5 Mg CO2e ha^?1 yr^?1). Nitrogen fertilizer did not affect net GHG mitigation potential or the contribution of roots to GHG mitigation for any bioenergy crop. SOC did not change and therefore did not contribute to GHG mitigation potential. However, associations among SOC, root biomass, and root C : N ratio suggest greater long‐term C storage in diverse polycultures vs. switchgrass. Carbon pools in roots have a greater effect on net GHG mitigation than SOC in the short‐term, yet variation in root characteristics may alter patterns in long‐term C storage among bioenergy crops.     

Estimating product and energy substitution benefits in national‐scale mitigation analyses for Canada

The potential of forests and the forest sector to mitigate greenhouse gas (GHG) emissions is widely recognized, but challenging to quantify at a national scale. Mitigation benefits through the use of forest products are affected by product life cycles, which determine the duration of carbon storage in wood products and substitution benefits where emissions are avoided using wood products instead of other emissions‐intensive building products and energy fuels. Here we determined displacement factors for wood substitution in the built environment and bioenergy at the national level in Canada. For solid wood products, we compiled a basket of end‐use products and determined the reduction in emissions for two functionally equivalent products: a more wood‐intensive product vs. a less wood‐intensive one. Avoided emissions for end‐use products basket were weighted by Canadian consumption statistics to reflect national wood uses, and avoided emissions were further partitioned into displacement factors for sawnwood and panels. We also examined two bioenergy feedstock scenarios (constant supply and constrained supply) to estimate displacement factors for bioenergy using an optimized selection of bioenergy facilities which maximized avoided emissions from fossil fuels. Results demonstrated that the average displacement factors were found to be similar: product displacement factors were 0.54 tC displaced per tC of used for sawnwood and 0.45 tC tC^?1 for panels; energy displacement factors for the two feedstock scenarios were 0.47 tC tC^?1 for the constant supply and 0.89 tC tC^?1 for the constrained supply. However, there was a wide range of substitution impacts. The greatest avoided emissions occurred when wood was substituted for steel and concrete in buildings, and when bioenergy from heat facilities and/or combined heat and power facilities was substituted for energy from high‐emissions fossil fuels. We conclude that (1) national‐level substitution benefits need to be considered within a systems perspective on climate change mitigation to avoid the development of policies that deliver no net benefits to the atmosphere, (2) the use of long‐lived wood products in buildings to displace steel and concrete reduces GHG emissions, (3) the greatest bioenergy substitution benefits are achieved using a mix of facility types and capacities to displace emissions‐intensive fossil fuels.     

Net climate impacts of forest biomass production and utilization in managed boreal forests

In this work, we studied the potentials offered by managed boreal forests and forestry to mitigate the climate change using forest‐based materials and energy in substituting fossil‐based materials (concrete and plastic) and energy (coal and oil). For this purpose, we calculated the net climate impacts (radiative forcing) of forest biomass production and utilization in the managed Finnish boreal forests (60°–70°N) over a 90‐year period based on integrated use forest ecosystem model simulations (on carbon sequestration and biomass production of forests) and life‐cycle assessment (LCA) tool. When studying the effects of management on the radiative forcing in a system integrating the carbon sink/sources dynamics in both biosystem and technosystem, the current forest management (baseline management) was used a reference management. Our results showed that the use of forest‐based materials and energy in substituting fossil‐based materials and energy would provide an effective option for mitigating climate change. The negative climate impacts could be further decreased by maintaining forest stocking higher over the rotation compared to the baseline management and by harvesting stumps and coarse roots in addition to logging residues in the final felling. However, the climate impacts varied substantially over time depending on the prevailing forest structure and biomass assortment (timber, energy biomass) used in substitution.     

Impacts of intensifying or expanding cereal cropping in sub‐Saharan Africa on greenhouse gas emissions and food security

Cropping is responsible for substantial emissions of greenhouse gasses (GHGs) worldwide through the use of fertilizers and through expansion of agricultural land and associated carbon losses. Especially in sub‐Saharan Africa (SSA), GHG emissions from these processes might increase steeply in coming decades, due to tripling demand for food until 2050 to match the steep population growth. This study assesses the impact of achieving cereal self‐sufficiency by the year 2050 for 10 SSA countries on GHG emissions related to different scenarios of increasing cereal production, ranging from intensifying production to agricultural area expansion. We also assessed different nutrient management variants in the intensification. Our analysis revealed that irrespective of intensification or extensification, GHG emissions of the 10 countries jointly are at least 50% higher in 2050 than in 2015. Intensification will come, depending on the nutrient use efficiency achieved, with large increases in nutrient inputs and associated GHG emissions. However, matching food demand through conversion of forest and grasslands to cereal area likely results in much higher GHG emissions. Moreover, many countries lack enough suitable land for cereal expansion to match food demand. In addition, we analysed the uncertainty in our GHG estimates and found that it is caused primarily by uncertainty in the IPCC Tier 1 coefficient for direct N₂O emissions, and by the agronomic nitrogen use efficiency (N‐AE). In conclusion, intensification scenarios are clearly superior to expansion scenarios in terms of climate change mitigation, but only if current N‐AE is increased to levels commonly achieved in, for example, the United States, and which have been demonstrated to be feasible in some locations in SSA. As such, intensifying cereal production with good agronomy and nutrient management is essential to moderate inevitable increases in GHG emissions. Sustainably increasing crop production in SSA is therefore a daunting challenge in the coming decades.     

Nitrogen rate and landscape impacts on life cycle energy use and emissions from switchgrass‐derived ethanol

Switchgrass‐derived ethanol has been proposed as an alternative to fossil fuels to improve sustainability of the US energy sector. In this study, life cycle analysis (LCA) was used to estimate the environmental benefits of this fuel. To better define the LCA environmental impacts associated with fertilization rates and farm‐landscape topography, results from a controlled experiment were analyzed. Data from switchgrass plots planted in 2008, consistently managed with three nitrogen rates (0, 56, and 112 kg N ha^?1), two landscape positions (shoulder and footslope), and harvested annually (starting in 2009, the year after planting) through 2014 were used as input into the Greenhouse gases, Regulated Emissions and Energy use in transportation (GREET) model. Simulations determined nitrogen (N) rate and landscape impacts on the life cycle energy and emissions from switchgrass ethanol used in a passenger car as ethanol–gasoline blends (10% ethanol:E10, 85% ethanol:E85s). Results indicated that E85s may lead to lower fossil fuels use (58 to 77%), greenhouse gas (GHG) emissions (33 to 82%), and particulate matter (PM2.5) emissions (15 to 54%) in comparison with gasoline. However, volatile organic compounds (VOCs) and other criteria pollutants such as nitrogen oxides (NOx), particulate matter (PM10), and sulfur dioxides (SO_x) were higher for E85s than those from gasoline. Nitrogen rate above 56 kg N ha^?1 yielded no increased biomass production benefits; but did increase (up to twofold) GHG, VOCs, and criteria pollutants. Lower blend (E10) results were closely similar to those from gasoline. The landscape topography also influenced life cycle impacts. Biomass grown at the footslope of fertilized plots led to higher switchgrass biomass yield, lower GHG, VOCs, and criteria pollutants in comparison with those at the shoulder position. Results also showed that replacing switchgrass before maximum stand life (10–20 years.) can further reduce the energy and emissions reduction benefits.